package uncertain.util;

import java.io.IOException;
import java.io.Reader;

/**
 * Migrated from StringReader ,remove sync-lock
 * 
 * @author jessen
 * 
 */
public class FastStringReader extends Reader {

	private String str;
	private int length;
	private int next = 0;
	private int mark = 0;

	/**
	 * Creates a new fast string reader.
	 * 
	 * @param s
	 *            String providing the character stream.
	 */
	public FastStringReader(String s) {
		this.str = s;
		this.length = s.length();
	}

	/**
	 * Reads a single character.
	 * 
	 * @return The character read, or -1 if the end of the stream has been
	 *         reached
	 * 
	 * @exception IOException
	 *                If an I/O error occurs
	 */
	public int read() throws IOException {
		if (next >= length)
			return -1;
		return str.charAt(next++);
	}

	/**
	 * Reads characters into a portion of an array.
	 * 
	 * @param cbuf
	 *            Destination buffer
	 * @param off
	 *            Offset at which to start writing characters
	 * @param len
	 *            Maximum number of characters to read
	 * 
	 * @return The number of characters read, or -1 if the end of the stream has
	 *         been reached
	 * 
	 * @exception IOException
	 *                If an I/O error occurs
	 */
	public int read(char cbuf[], int off, int len) throws IOException {
		if ((off < 0) || (off > cbuf.length) || (len < 0)
				|| ((off + len) > cbuf.length) || ((off + len) < 0)) {
			throw new IndexOutOfBoundsException();
		} else if (len == 0) {
			return 0;
		}
		if (next >= length)
			return -1;
		int n = Math.min(length - next, len);
		str.getChars(next, next + n, cbuf, off);
		next += n;
		return n;
	}

	/**
	 * Skips the specified number of characters in the stream. Returns the
	 * number of characters that were skipped.
	 * 
	 * <p>
	 * The <code>ns</code> parameter may be negative, even though the
	 * <code>skip</code> method of the {@link Reader} superclass throws an
	 * exception in this case. Negative values of <code>ns</code> cause the
	 * stream to skip backwards. Negative return values indicate a skip
	 * backwards. It is not possible to skip backwards past the beginning of the
	 * string.
	 * 
	 * <p>
	 * If the entire string has been read or skipped, then this method has no
	 * effect and always returns 0.
	 * 
	 * @exception IOException
	 *                If an I/O error occurs
	 */
	public long skip(long ns) throws IOException {
		if (next >= length)
			return 0;
		// Bound skip by beginning and end of the source
		long n = Math.min(length - next, ns);
		n = Math.max(-next, n);
		next += n;
		return n;
	}

	/**
	 * Tells whether this stream is ready to be read.
	 * 
	 * @return True if the next read() is guaranteed not to block for input
	 * 
	 * @exception IOException
	 *                If the stream is closed
	 */
	public boolean ready() throws IOException {
		return true;
	}

	/**
	 * Tells whether this stream supports the mark() operation, which it does.
	 */
	public boolean markSupported() {
		return true;
	}

	/**
	 * Marks the present position in the stream. Subsequent calls to reset()
	 * will reposition the stream to this point.
	 * 
	 * @param readAheadLimit
	 *            Limit on the number of characters that may be read while still
	 *            preserving the mark. Because the stream's input comes from a
	 *            string, there is no actual limit, so this argument must not be
	 *            negative, but is otherwise ignored.
	 * 
	 * @exception IllegalArgumentException
	 *                If readAheadLimit is < 0
	 * @exception IOException
	 *                If an I/O error occurs
	 */
	public void mark(int readAheadLimit) throws IOException {
		if (readAheadLimit < 0) {
			throw new IllegalArgumentException("Read-ahead limit < 0");
		}
		mark = next;
	}

	/**
	 * Resets the stream to the most recent mark, or to the beginning of the
	 * string if it has never been marked.
	 * 
	 * @exception IOException
	 *                If an I/O error occurs
	 */
	public void reset() throws IOException {
		next = mark;
	}

	/**
	 * Closes the stream and releases any system resources associated with it.
	 * Once the stream has been closed, further read(), ready(), mark(), or
	 * reset() invocations will throw an IOException. Closing a previously
	 * closed stream has no effect.
	 */
	public void close() {
		str = null;
	}
}
